Sulphur-35 radiotracer studies of the effect of hydrogen sulphide on a molybdenum disulphide catalyst in the hydrogenation of buta-1,3-diene

Abstract

Hydrogenation of buta-1,3-diene on a molybdenum disulphide catalyst has been studied in order to determine the change in the pattern of butene product distribution with catalyst treatment (with hydrogen, a buta-1,3-diene + hydrogen mixture, air, hydrogen sulphide or a thiophene + hydrogen mixture). Catalyst treatment with sulphur compounds (H₂S or thiophene + H₂) resulted in a butene product distribution closer to thermodynamic equilibrium proportions than for a catalyst treated with hydrogen or air. ³⁵S has been used as a tracer in H₂S to measure the quantity of H₂S necessary to change the catalytic function on fresh and hydrogen-treated catalysts and to observe the extent of sulphur isotopic exchange of gas-phase H₂S with MoS₂-lattice sulphur and with adsorbed H₂S. Evidence is presented for the participation in the hydrogenation reaction of hydrogen present as adsorbed HS groups on the MoS₂ surface, and the change of catalytic function with H₂S treatment has been interpreted in terms of the change in distribution of these HS groups.